Synthesis of hydroxylated hexahydropyrrolo[2,1-b]thiazoles

An unexpected ring contraction of 7,5-fused bicyclic thiazolidinelactams yields hexahydropyrrolo2,1-b]thiazoles in a single synthetic step. Three stereocentres are inverted along the highly stereoselective reaction path. The title compounds are further transformed into thio-analogues of polyhydroxylated pyrrolizidine alkaloids.